The present invention relates to electric batteries comprising at least one electric cell and more particularly to lead-acid batteries such as sealed, gas recombining lead-acid batteries which may for example be used in standby applications such as telephone exchanges, uninterruptable power supplies, power stations and emergency lighting systems.
Sealed gas recombining lead-acid batteries are already known. These batteries operate in such a manner that gases normally evolved on overcharge are chemically recombined, thus completely eliminating water loss. In a conventional lead-acid battery, water is electrolysed on overcharge liberating oxygen at the positive electrodes and hydrogen at the negative electrodes. In a sealed recombination cell, the stoichiometry of active materials is such that the positive plate becomes fully charged before the negative, and oxygen is liberated which diffuses to the negative plate where it reacts with lead to form lead oxide. The lead oxide then reacts with the sulphuric acid electrolyte to form lead sulphate and water. Oxygen transport from the positive to the negative plate is made possible by the use of a highly porous glass microfibre separator which is not fully saturated with electrolyte and allows oxygen to diffuse readily between the plates through interconnected pores free of electrolyte. The battery operates under an internal pressure and has a physically tight assembly, to ensure efficient recombination.